No modifications of any kind allowed to any part of the car unless specified.  Any existing car that is unapproved will be allowed to race if it meets all safety requirements.  Any car that is unapproved, and is deemed to have an advantage will be penalized.

The thunder stock class will be open to any North American made 2 or 4 door hardtop or sedan, 1960 or newer, with a wheelbase no less than 113 with 1/2” tolerance.

All burnable material, lights and white metal must be stripped from the car.

All glass other than the windshield must be removed.

The firewalls must be patched with minimum twenty gauge steel to seal them.  Fire suppression system recommended.

All body parts must be stock and mounted in the stock way exceptions will be made for replacing stock fiberglass with sheet metal. Doors must be chained, bolted or welded shut.  Hood and truck lid must be securely fastened.

Sunroofs and T-tops must be enclosed.

No gutting of vehicle allowed except room for door bars.

Front inner wheel wells may be removed, but only what can be unbolted, no cutting out of any material other than 2” radius around wheel wells for tire clearance.

Minimum car weight must be no less than 3400lb with the driver.  All ballasts must be painted white and marked with car number.  Race officials may ask any car with an advantage to add extra weight.

All sharp edges, torn fenders, bumpers and body panels are to be repaired prior to next race date.

Station wagon vehicles and 1/2 ton trucks allowed in Thunder class.

Any body repairs can be sheeted in with ordinary body metal.



Stock bumpers mounted with stock mounts in stock locations.

Bumpers must be safely chained to keep them from separating from the car.

One straight tube, maximum of 2” O.D. can be welded directly behind the front bumper and in front of the rear bumper, between the frame rails.

Metal gouge guards must be installed and attached from bumper to body panel.

No cutting of bumpers.

Easily accessible tow chains must be mounted to the frame or bumper on the front and rear of the car.

Bumperettes must be removed.



Stock suspension only for year, make and model of car allowed.  All replacement parts must be stock replacement parts.  No modifications or exchanging of parts between makes and models allowed, unless for safety reasons.

Stock mounting locations for shocks.  Only one shock per wheel.  Racing Shocks are allowed.

Stock mounting locations for springs only

Anti-sway bars cannot be adjustable and must be equally spaced side to side.

Body bushings must be stock.

Front alignment may be set to drivers preference, but no modifications are allowed to any part to improve alignment over stock adjustment.




Aluminium radiators allowed, must be in stock location with stock type mounts.



Must be stock unmodified differential for year, make and model of car.  Spider gears may be welded.  No spools allowed.

 No locked, limited slip or posi-traction units allowed unless a stock limited slip.

 Gear ratio must be a stock ratio for the year, make and model of the car.



Stock type unmodified automatic transmissions only.  No standard transmissions. Transmission blanket/scattershield recommended but not mandatory.

  Stock type unmodified torque converter.

Must have all gears operational at the beginning of race day. Eg: Th350 must have 3 forward and 1 reverse; PG 2 forward and 1 reverse.

All drive shafts must be steel, painted white and have a safety hoop (can be 1/4 inch chain) near the front of the driveshaft and within 12 inches of the u-joint.



The tires must be DOT approved radial passenger car all season.  No ground grips or open lug tires.  No racing brand tires eg: McCreary, Hoosier etc.

All wheels must be of steel construction.  Maximum 8” wheel allowed.  No aluminum or magnesium wheels allowed.

No bead lock or wheel spacers allowed.

Steel wheel studs only, 1/2” studs recommended.

Stud threads must be extended past the nut when rim is mounted.

1” lug nuts are mandatory.



All roll cage material must be minimum 1.66 O.D. steel tubing with a minimum .095 wall thickness, minimum 6 point cage.

All joints must be welded 360 degrees.

All roll cages must be attached to the frame with a minimum of 1 horizontal cross brace.  Drivers helmet must be below the roll cage.

A bar must be added to the center of the roof hoop for added protection.

3 horizontal drivers side door bars must be used on the passenger side of the drivers compartment.

Drivers side pillar bar is mandatory.

1 bar is allowed to run through the front firewall, on drivers side for leg protection.

All major joints must be gusseted and triangulated.

Drivers door bars must have 18 gauge anti-penetration plate covering all holes from the front pillar bar to the back pillar bars closing the holes between the 3 horizontal door bars.


Front Hoops are Allowed.


All seats must be racing type seats.

Seat belts are to be racing type 5 point 3” width mounted securely to the frame, seat frame and roll cage.  All belts must be mounted as per manufacturers specs, and be in good condition (no frays, cuts or sun fading).  Shoulder pads recommended.

Driver side quick release window net is mandatory, mounted securely to the roll cage.

All cars must have a screen (max 2” square and min. 10 gauge wire or equivalent) with 2 minimum 5/8” bars in the center opening.

Battery must be mounted securely.  It must be encased in a marine style box if mounted in the drivers compartment.

Fuel tanks must be mounted inside the trunk, and securely fastened.  No tanks larger than 15 gallons are allowed.  Boat tanks are allowed.  Fuel cells recommended.  Protected by 1.66 O.D. steel tube hoop, mounted to the frame rails between the fuel cell and tail panel.  Rollover spill protection is mandatory.

All cars MUST have an operable 2lb minimum fire extinguisher mounted in a quick release bracket in reach of drivers at all times.  Each pit area MUST have an operable 5lb ABC fire extinguisher.

Drivers must wear minimum SFI 3.2 racing suit mandatory.  *Helmet to be minimum SA2000 with full face shield.  No dirt bike/snow cross helmets.

Each car must have a clearly labeled kill switch which is easily accessible from the outside of the car.  It must kill ALL electrical power to the vehicle.

All cars must have 2 clearance lights, red in color, one in each corner of the vehicles back window.

If running an electrical fuel pump, there must be a separate pump shut off switch within reach of the driver, and an oil pressure controlled pump disconnect(Hobbs switch) to interrupt the circuit when the motor stops.

Neck braces mandatory, Hans device strongly recommended.



Absolutely stock for year, make and model.  If an engine change is required for reliability, maximum engine size allowed is 350 Chev, 351 Ford, and 360 Dodge with a .040 oversize allowed within the same manufacturer family lines.  Engines must remain stock and must be 2 barrel with replacement engine.  Then engine displacement has been changed from stock by exercising this rule, the maximum allowed carb is 500cfm Holley.

The choke plate may be removed.

Exhaust must exit behind the driver.  Mufflers and converters may be removed.  Maximum pipe allowed is 2 1/2", strongly recommended both pipes exit passenger side.

Engines must be adequately tethered on BOTH sides.

After market hydraulic Camshaft will be allowed providing factory idle is maintained smoothly and manifold vacuum maintained at 15” at stock idle rpm.

Exhaust manifold replacement short tube headers will be allowed in lue of exhaust manifolds.

If you are running the aftermarket cam and/or the short tube headers you must run a two barrel carborater. 



Absolutely stock for year, make and model of car.

All 4 brakes must operational.

Yellowhead International Speedway